1. Field of the Invention
The present invention relates to an image stabilization control circuit incorporated in an image pickup apparatus.
2. Description of the Related Art
Recently, in image pickup apparatuses such as digital still cameras and digital video cameras, the number of pixels of an image sensing device provided therein is increased to achieve a higher image quality. Meanwhile, as another method of achieving a higher image quality in the image pickup apparatuses, it is desirable that the image pickup apparatuses are provided with a hand-shake correction function in order to prevent a blurred image of an object caused by shaking of the hand holding the image pickup apparatus.
To be specific, the image pickup apparatus comprises a detection element such as a gyro sensor or the like, and prevents a blurred image of an object by driving an optical component such as a lens and an image sensing device in response to an angular velocity component generated by vibration of the image pickup apparatus. Accordingly, even if the image pickup apparatus is shaken, a vibration component is not reflected in an obtained image signal, and an image signal of high image quality having no image blur can be obtained.
FIG. 4 is a block diagram of a conventional image stabilization control circuit 100 used for achieving the hand-shake correction function. The image stabilization control circuit 100 is provided in the image pickup apparatus, and operates according to control by a main control circuit (not shown) provided in the image pickup apparatus. The image stabilization control circuit 100 is connected to a position detecting element 102, a lens driving element 104, and a vibration detecting element 106.
The position detecting element 102 detects the position of a lens used in the image pickup apparatus. A hall element can be used as the position detecting element 102, and generates an induced current corresponding to an absolute position of the lens and outputs a voltage signal. A voice coil motor can be used as the lens driving element 104. The image stabilization control circuit 100 adjusts a voltage value applied to the lens driving element 104 to control the position of a moving coil of the voice coil motor, namely, the position of the lens with respect to a standard optical axis. The lens driving element 104 drives the lens in a plane perpendicular to the standard optical axis of the image pickup apparatus. The vibration detecting element 106 detects vibration of the image pickup apparatus and outputs the result to the image stabilization control circuit 100. A gyro sensor can be used as the vibration detecting element 106, which generates an angular velocity signal corresponding to vibration applied to the image pickup apparatus and outputs the angular velocity signal to the image stabilization control circuit 100.
It is preferable that the position detecting element 102, the lens driving element 104, and the vibration detecting element 106 are respectively constituted by at least two elements. For example, a plurality of elements for a horizontal component and a vertical component are provided in a plane perpendicular to the optical axis of the image pickup apparatus to detect the position of the lens, move the lens, and detect the vibration of the image pickup apparatus.
Next, the image stabilization control circuit 100 will be described in detail. The image stabilization control circuit 100 comprises a servo circuit 10, a lens driver 12, an analog-digital converter circuit (ADC) 14, a CPU 16, and a digital-analog converter circuit (DAC) 18.
The servo circuit 10 generates a signal for controlling the lens driving element 104 according to the voltage signal output from the position detecting element 102. The servo circuit 10 comprises an analog filter circuit having an external resistance element, a capacitor or the like, and generates a signal for controlling the lens driving element 104 such that the optical axis of the lens corresponds to the center of an image sensing device provided in the image pickup apparatus. The lens driver 12 generates a lens driving signal for driving the lens driving element 104 based on the signal output from the servo circuit 10.
The ADC 14 converts the analog angular velocity signal output from the vibration detecting element 106 to a digital signal. The CPU 16 generates an angle signal representing a moving amount of the image pickup apparatus based on the digital angular velocity signal. The CPU 16 is connected to a memory (not shown) and performs the processing of generating the angle signal based on software stored in the memory. The DAC 18 converts the digital angle signal generated in the CPU 16 to an analog signal.
The servo circuit 10 generates a lens driving signal for driving the lens driving element 104 according to a signal obtained by adding the analog angle signal output from the DAC 18 to the voltage signal output from the position detecting element 102. In other words, in order to prevent a blurred image of an object by hand-shake, the position of the lens is changed based on the angle signal representing the moving amount of the image pickup apparatus to suppress the blurring of an object image on the image sensing device. Accordingly, an image signal of high image quality can be obtained by suppressing the blurring of an object image by hand-shake.
In order to improve the degree of freedom for adjusting the image stabilization control circuit, it is desirable to replace the servo circuit and the processing circuits of the vibration detection signal with a logic circuit capable of digital processing. To be specific, if a mechanism of a digital camera in which the image stabilization control circuit is provided is changed, it is necessary to change an adjustment value of the image stabilization control circuit, and it is required that the adjustment can be easily performed. Moreover, since the image stabilization control circuit is incorporated in the image sensing device such as a digital camera and a lens module of the image sensing device, the image stabilization control circuit needs to be reduced in size as much as possible even when the logic circuit is employed therein.